Field of the Invention
The present invention relates to a display apparatus, a light-emitting device, and a control method of a display apparatus, and in particular, relates to a suitable technique used to achieve both the visibility of a moving image and the prevention of flicker in a display apparatus in which a light-emitting device emits light to display an image on a hold-type display device such as a liquid crystal panel.
Description of the Related Art
Conventionally, if a display apparatus using a liquid crystal panel displays an image with movement, image retention called motion blur occurs. Thus, generally, display is performed by multiplying a frame frequency of 60 Hz or 50 Hz by a constant value, and also hold time is shortened to eliminate the influence of motion blur caused by the hold time.
To multiply the frame frequency by a constant value, it is required to generate intermediate image data to be displayed in a new frame. If, however, the original image includes image data having a striped pattern, intermediate image data is erroneously generated, which causes a sense of distortion in an image.
On the other hand, if the hold time is consistently shortened with the frame frequency remaining at 60 Hz or 50 Hz to reduce motion blur, flicker occurs. This makes the resulting image difficult to see.
Particularly with a master monitor or a picture monitor used to check an image, the hold time is fixed to a value of about 50% as a percentage in one frame time (a duty ratio). The fixed duty cycle causes motion blur in a fast moving portion or causes flicker in a bright image, depending on the image.
Thus, it is required to minimize the occurrence of motion blur and flicker with the frame frequency remaining at 60 Hz or 50 Hz. Further, it is also required to make inconspicuous the sense of obstruction caused by the intermediate image data generated when the frame frequency is multiplied by a constant value.
Japanese Patent Application Laid-Open No. 2006-189658 and Japanese Patent Application Laid-Open No. 2011-13558 discuss a technique for detecting a motion vector and controlling hold time according to the detected motion vector. Japanese Patent Application Laid-Open No. 2012-78590 discusses a technique for detecting a motion vector and controlling hold time for each block of a backlight according to the detected motion vector. Japanese Patent Application Laid-Open No. 2009-251069 discusses a technique for controlling hold time based on the luminance level of a partial area in display.
However, to control the hold time (duty ratio) of light emission using a motion vector, there is no choice but to shorten the hold time in a case of an image with great movement. If the hold time is shortened in a single light emission, flicker occurs in a case of a bright image. If light emission is repeated twice with a short hold time to prevent flicker, a portion with movement is seen twice, and an obstruction called double blurring (i.e., ghosting) appears.
Further, to control the hold time based on the luminance level of a partial area in display, there is no choice but to lengthen the hold time in an image including a bright area. However, this causes motion blur in a portion with movement.